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One of the Most Complex and Ambitious Ventures in the History of Space Exploration
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Saturn Controls a Giant Planetary System
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Exploring Saturn nameplate
Saturn by Cassini
Saturn is the second largest planet in our Solar System. It is the sixth planet outward from the Sun.

At a distance of some 900 million miles, Saturn is almost twice as far from the Sun as the planet Jupiter.

From Saturn, the Sun appears ten times smaller than it appears from Earth. An average area on Earth receives 90 times the amount more sunlight than the same area on Saturn.

Being farther from the Sun, Saturn is much colder than Jupiter, with an average temperature around –285°F.

Somewhat like our Solar System of which it is a part, Saturn has its own system, including spectacular rings and the second greatest collection of moons in the Solar System including the second largest moon in the Solar System.

The planet is named for the ancient Roman god of agriculture. The English word Saturday comes from the word Saturn.

Take a look. Saturn is seen easily without a telescope. In fact, people have being seeing Saturn in the nighttime sky since before history. Today, Saturn's rings and larger satellites can be seen with a small telescope. By the way, it's easy to identify Saturn as a planet because its light is steady. It doesn't twinkle like the stars.



What Is It Made Of?
It is not a rock like Earth. Saturn is not solid at all. It doesn't have a surface. You couldn't land there because there is nothing solid to land on. If there is something at the center, it might be a teeny core of rock surrounded by a liquid and then smothered by the very deep atmosphere.

Saturn is a giant cloud of mostly hydrogen and helium gases. Gravity, the same force that brings things down to Earth, holds the gases of Jupiter together. Billions of years ago, there may have been several huge clouds of gas that came together. As the combined cloud got bigger, it gathered up more gas. The larger it grew, the stronger its gravity became.

Saturn may not have land, but it does have weather. With clouds swirling through the atmosphere ahead of 1,000 mph winds, storm patterns could be ever-changing.
Big ol' gas bag. Astronomers refer to four of the Solar System's outer planets as gas giants – Jupiter, Saturn, Uranus and Neptune.

Saturn, which formed more than four billion years ago, is mostly hydrogen and helium gases. There are lesser amounts of methane and ammonia. Saturn is a big ball of gas almost 75,000 miles in diameter held together by the pull of gravity. Hydrogen and helium also are the main gases in the Sun.

While almost as big in size as Jupiter, Saturn's mass is only 30 percent of Jupiter's mass. And its density is lowest in the Solar System. It's so low, in fact, that it would float in a bathtub if only we had a big enough tub.

Saturn doesn't have a solid surface of hard ground that we could walk on. What we see through telescopes is not a surface, but actually the top layer of a cloud of ammonia ice crystals.

Saturn's interior certainly is quite hot. The core temperature probably is 21,150°F. In fact, Saturn radiates more energy into space than it receives from the Sun.

Saturn's core may be rocky and about the size of the planet Earth. Above that hard core may be a liquid metallic hydrogen layer and a molecular hydrogen layer. Various ices also may be present.

Saturn looks yellow to us because it is reflecting light from the Sun. Small amounts of impurities within the ammonia cause the other colors we see in Saturn's cloud tops.

Winds are extreme at Saturn's equator where they can reach speeds greater than 1,100 mph. By comparison, the strongest hurricane winds on Earth reach 246 mph. Saturn's winds combine with heat from the planet's interior to spawn the yellow and gold bands we see in the planet's atmosphere.

The clouds tops are quite cold at around –400°F. Interestingly, the ammonia might be frozen and rain down from the clouds at –300°F..

The planet is surrounded by an enormous magnetic field. Like a huge bubble, this magnetosphere traps and holds electric particles near the planet.

The planet spins so fast, a day on Saturn lasts just over 10 hours. Because the planet is so far from the center of the Solar System, it takes Saturn almost 30 years to make a trip around the Sun.



About Moons...
A moon is a natural satellite rotating around a planet. While moons vary in size, each moon is much smaller than its planet.

Several moons are larger than the planet Pluto and two moons are larger than the planet Mercury. There also are many small moons that may be asteroids captured by their planets.

Only Mercury and Venus do not have any moons. By comparison, Earth has one moon and Mars has two. Jupiter has the most moons of any planet. Saturn is second.

Pictures taken by the Hubble Space Telescope suggest there may be even more moons around those outer planets.

LIST OF ALL PLANETS AND THEIR MOONS »»
The Moons. Saturn's moons are Titan, Rhea, Iapetus, Dione, Tethys, Enceladus, Mimas, Hyperion, Prometheus, Pandora, Phoebe, Janus, Epimetheus, Helene, Telesto, Calypso, Atlas, Pan, Ymir, Paaliaq, Siarnaq, Tarvos, Kiviuq, Ijiraq, Thrym, Skadi, Mundilfari, Erriapo, Albiorix, Suttung, and others yet to receive names.
list of saturn moons »

When the Cassini spacecraft from Earth arrived at Saturn in 2004, it promptly found two previously unseen moons. They turned out to be the smallest bodies seen around the ringed planet up to that time.

The tiny natural satellites are about 2 miles and 2.5 miles in diameter. That's smaller than the city of Boulder, Colorado. Previously, the smallest moons seen around Saturn were are about 12 miles across. The moons are 120,000 miles and 131,000 miles from the center of planet Saturn between the moons Mimas and Enceladus.

The newly discovered bodies were labeled S/2004 S1 and S/2004 S2. Later, they will be given names. The NASA JPL team wondered if S/2004 S1 might not be an object called S/1981 S14 that had turned up in a 1981 Voyager image.

Each of Saturn's known moons is unique. Here are some examples:


Exploring Saturn nameplate
Saturn's rings by Cassini
The Rings. The big planet is known for its dramatic rings. People often refer to it when they say, "the ringed planet." Of course, some other planets have rings.

Why are there rings around planets? It's not clear. Rings are not stable so they must rebuild themselves regularly. Saturn's current set of rings probably are only a few hundred million years old.

There are several rings around Saturn, each different from the others.
list of saturn rings »

Three rings known as A, B and C can be seen from Earth: The rings are not perfectly circular and the gaps between the rings are not entirely empty. Voyager saw spokes and braids in the rings. Cassini has seen spirals. These mysteries may relate to Saturn's magnetic field.

Four previously unknown, faint rings turned up in photographs sent back the Voyager spacecraft in the 1980s.

The outermost ring, labeled F, actually is several smaller rings with some knots of clumped material. Could the knots be tiny moons?

Saturn's rings were believed to be unique until 1977 when very faint rings were discovered around the planet Uranus. Shortly after that, other rings were seen around the planets Jupiter and Neptune.



Saturn Closest to Earth
The planet Saturn was relatively close to Earth on December 31, 2003, when it was about 746 million miles away. The sunlight reflected from the planet caused it to appear brighter than usual to observers on Earth. Saturn won't be that close to Earth again until 2032.
Robot Explorers. Saturn has been visited by several interplanetary probes from Earth. The first was Pioneer 11 in 1979.

Later, Saturn was visited by twin spacecraft from Earth known as the Voyagers. In fact, most of what we knew about Saturn and its system of moons and rings for two decades was learned when Voyager 1 flew by Saturn in 1980 and when Voyager 2 flew by Saturn in 1981.

The robot explorers Cassini and Huygens arrived in the Saturn system on July 1, 2004. Huygens did its job in 2005 while Cassini will work among the moons and rings until at least 2008. Now we are learning a great deal more about the beautiful ringed planet.
LATEST NEWS FROM CASSINI »»



List of Moons and Rings. Here the natural satellites of Saturn and the rings around the planet:

Moons of Saturn
NAMEDISCOVERED
Iapetus1671
Rhea1672
Tethys1684
Dione1684
Titan1655
Mimas1789
Enceladus1789
Hyperion1848
Phoebe1898
Janus1966
Atlas1980
Prometheus1980
Pandora1980
Epimetheus1980
Telesto1980
Calypso1980
Helene1980
Pan1990
Ymir2000
Paaliaq2000
Siarnaq2000
Tarvos2000
Kiviuq2000
Ijiraq2000
Thrym2000
Skadi2000
Mundilfari2000
Erriapo2000
Albiorix2000
Suttung2000
S/2003 S 12003
S/2004 S 12004
S/2004 S 22004
Rings of Saturn
NAME
ring or gap
DISTANCE
kilometers
WIDTH
kilometers
D Ring63,50011,000
Guerin Division  
C Ring74,50017,600
Maxwell Division87,750500
B Ring92,10025,300
Cassini Division117,4004,700
Huygens Gap117,680300-400
A Ring122,10014700
Encke Minima127,5003,500
Encke Division133,500 
Keeler Gap136,500 
F Ring140,210 
G Ring165,8008,000
E Ring180,000300,000





LIST OF ALL PLANETS AND THEIR MOONS »»

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